1. Field of the Invention
This invention relates generally to bending machines and equipment for bending lengths of pipe used in oil, gas, water, and other types of transmission pipelines and specifically to bending dies used in pipe bending machines.
2. Background of the Invention
Conventional dies used in pipe bending machines include half-cylindrical geometries machined so as to have a curve along their length. The radius of curvature of these dies depends upon the diameter of the pipe and have been determined over time. Such radii of curvature as well as known information relating to the recommended degrees of bend are known in the art and can be found on various tables.
A substantial defect inherent in conventional dies is the fact that in practice, the bending force applied is concentrated at one point along the rigid die thereby creating the effect of bending the pipe over a transverse cylinder as opposed to a radius of curvature. The result being the creation of a hot spot on the pipe where the bend occurs. At this spot the pipe weakens from being stretched and also tends to oval in cross-section.
If the bending machine operator is not careful and attentive and pulls too much of a bend, the pipe is known to wrinkle at this hot spot rendering it unusable. The wrinkled section must then be cut out creating waste of very expensive pipe material. As a matter of caution, recommended degrees of bend are small using only a small stroke of the hydraulic cylinders of the bending apparatus. Substantial bends over shorter lengths of pipe result. A need, therefore, exists for a die assembly which includes a flexible die portion to distribute the bending force over a longer length of the pipe thereby creating a uniform bend without hot spots and their attendant ovalization or weakening of the pipe wall. A further need exists for such a die which will further allow greater degrees of bend over longer segments of pipe.
The die assembly of the present invention includes three major components, an exterior housing, a flexible die, and an eggcrate assembly. The exterior housing encompasses the flexible die and eggcrate assembly and pins into conventional bending machines.
The flexible die includes a plurality of plate segments positioned along a pair of tie rods. Each plate segment is narrow in width and is hung on the tie rods so as to be free floating thereon. The plate segments are arranged so as to provide a space between adjacent plate segments such that flex of the tie rods causes the plate segments to converge on the end in the direction of the flex and diverge (accordian) in the direction opposite the flex.
The eggcrate assembly provides a support for a plurality of spring plates. Each spring plate has a radius of curvature consistent with the amount of bend desired in the pipe. During the bending process, a force is applied by the stiffback of the bending machine against the pipe. The pipe in turn forces the flexible die in contact with the spring plates of the eggcrate assembly. Since each plate segment is independent and free floating on the tie rods, the bending force exerted by the die to the pipe is distributed among the plate segments thereby creating a uniform bend. A plurality of liner bars may be positioned between the plate segments and the pipe to further distribute the force evenly over a greater length of pipe than the conventional die.
An object of the present invention is therefore to provide a die assembly with a flexible die that distributes the bending force over the entire bend.
A further object of the present invention is to provide such a die assembly which may be retrofit into conventional pipe bending machines.
Further objects and advantages of the present invention will become apparent from the specification and claims.